1. Field of the Invention
This invention relates to a chip-type solid electrolytic capacitor, and more particularly to an electrode-structure having an improved connection reliability of an anode terminal.
2. Description of the Prior Art
To improve a volumetric efficiency of a conventional molded chip-type solid electrolytic capacitor, non-molded chip-type solid electrolytic capacitor is proposed in Japanese Published Patent No. Sho.61-31609 (1986), as shown in FIG. 1. A capacitor element 10 with an insulating resin 6 except for a bottom portion to expose a cathode layer. Each end surface of a capacitor element is coated with a conductor layer 14a and 14b as of silver paste, electroless plated layers 15a and 15b as of nickel, and solder layers 16a and 16b successively. An anode lead 2 is provided with a notch and finally folding the anode lead at the notch to cut it there.
However, because of the longer projection of the anode lead, a part-installing apparatus may cause accident such as snapping off by pawls of the apparatus during setting the capacitor to the printed wiring board or the like. This is for the reason that in the method making the notch by a cutting blade, the thinning of the cutting blade is limited to well keep the mechanical strength of the cutting blade and therefore it is impossible to cut thinner than this thickness. Another reason is that it is needed to take enough long cutting size to prevent the conductive layer on the anode lead from peeling from it due to the mechanical stress while cutting.
It has further disadvantage that because of the bonding through the intervention of the Van der Waals force between the anode lead and the electroless plated layer, the bonding strength becomes decreased due to mechanical and thermal stresses during part-installing process, and the tangent of the dielectric loss (referred to as tan .delta. hereinafter) becomes increased.
For the purpose of improving this, for example, a method is proposed for enhancing the adhesive strength which comprises making a partial surface of the anode lead rough by the sand blast technique or the like, and then forming an electroless plating layer, as disclosed in the above Japanese Patent. This however presents problems not only of complicating process but also which may cause damage of the conversion coating and increase in leakage current by impingement while blasting.